1. Technical Field
The present disclosure relates to a light emitting diode (LED) and method for making the same.
2. Description of Related Art
In recent years, highly efficient LEDs made with GaN-based semiconductors have become widely used in different technologies, such as in display devices, large electronic billboards, street lights, car lights, and other illumination applications. LEDs are environmentally friendly, have a long working life, and low power consumption.
A conventional LED commonly includes an N-type semiconductor layer, a P-type semiconductor layer, an active layer, an N-type electrode, and a P-type electrode. The active layer is located between the N-type semiconductor layer and the P-type semiconductor layer. The P-type electrode is located on the P-type semiconductor layer. The N-type electrode is located on the N-type semiconductor layer. Typically, the P-type electrode is transparent. In operation, a positive voltage and a negative voltage are applied respectively to the P-type semiconductor layer and the N-type semiconductor layer. Thus, cavities in the P-type semiconductor layer and electrons in the N-type semiconductor layer can enter the active layer and combine with each other to emit visible light.
However, extraction efficiency of LEDs is low because typical semiconductor materials have a higher refractive index than that of air. Large-angle light emitted from the active layer may be internally reflected in LEDs, so that a large portion of the light emitted from the active layer remains in the LEDs, thereby degrading the extraction efficiency.
What is needed, therefore, is a LED which can overcome the above-described shortcomings.